Additive printed mask process and structures produced thereby

ABSTRACT

A digital lithographic process first deposits a mask layer comprised of print patterned mask features. The print patterned mask features define gaps into which a target material may be deposited, preferably through a digital lithographic process. The target material is cured or hardened, if necessary, into target features. The mask layer is then selectively removed. The remaining target features may then be used as exposure or etch masks, physical structures such as fluid containment elements, etc. Fine feature widths, narrower the minimum width of the print patterned mask features, may be obtained while realizing the benefits of digital lithography in the manufacturing process.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention is related to copending U.S. Application forLetters Patent titled “Process For Forming A Feature By Undercutting APrinted Mask” by Limb et al., Ser. No. 11/336,365, filed Jan. 20, 2006and assigned to the same assignee as the present application, andfurther which is hereby incorporated herein by reference.

The present application is a continuation of application Ser. No.10/536,102, filed Jan. 20, 2006, to which priority is claimed and whichis incorporated by reference herein.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

This invention was made with government support under contract number70NANB3H3029 (Novel x-Ray) awarded by the U.S. Government NationalInstitute of Standards and Technology—ATP. The government has certainrights in the invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to electronic device fabricationprocesses, and more particularly to a method of employing a printed maskto form features narrower than the printed mask feature width.

2. Description of the Prior Art

Digital lithography is a maturing technology designed to reduce thecosts associated with photolithographic processes, used often in thefabrication of micro-electronic devices, integrated circuits, andrelated structures. Digital lithography directly deposits patternedmaterial onto a substrate in place of the delicate and time-consumingphotolithography processes used in conventional manufacturing processes.The printed pattern produced by digital lithography can either compriseactual device features (i.e., elements that will be incorporated intothe final device or circuitry, such as the source, drain, and gateregions of thin film transistors, signal lines, opto-electronic devicecomponents, etc.) or it can be a mask for subsequent semiconductorprocessing (e.g., etch, implant, etc.) Importantly, unlike traditionallithographic systems, digital lithography systems avoid the cost andchallenges associates with the use of reticles or masks.

Typically, digital lithography involves depositing a print material bymoving a printhead and a substrate relative to one another along asingle axis (the “print travel axis”). Print heads, and in particular,the arrangements of the ejectors incorporated in those print heads, areoptimized for printing along this print travel axis. Printing takesplace in a raster fashion, with the print head making “printing passes”across the substrate as the ejector(s) in the print head dispenseindividual “droplets” of print material onto the substrate. Typically,the print head moves relative to the substrate in each printing pass,but the equivalent result may be obtained if the substrate is caused tomove relative to the print head (for example, with the substrate securedto a moving stage) in a printing pass. At the end of each printing pass,the print head (or substrate) makes a perpendicular shift relative tothe print travel axis before beginning a new printing pass. Printingpasses continue in this manner until the desired pattern has been fullyprinted onto the substrate.

Materials typically printed by digital lithographic systems includephase change material and solutions of polymers, colloidal suspensions,such suspensions of materials with desired electronic properties in asolvent or carrier. For example, U.S. Pat. Nos. 6,742,884 and 6,872,320(each incorporated herein by reference) teach a system and process,respectively, for printing a phase change material onto a substrate formasking. According to these references, a suitable material, such as astearyl erucamide wax, is maintained in liquid phase over an ink-jetstyle piezoelectric printhead, and selectively ejected on adroplet-by-droplet basis such that droplets of the wax are deposited indesired locations in a desired pattern on a layer formed over asubstrate. The droplets exit the printhead in liquid form, then solidifyafter impacting the layer, hence the material is referred to asphase-change.

Once dispensed from an ejector, a print material droplet attaches itselfto the substrate through a wetting action, then proceeds to solidify inplace. In the case of printing phase-change materials, solidificationoccurs when a heated and liquefied printed droplet loses its thermalenergy to the substrate and/or environment and reverts to a solid form.In the case of suspensions, after wetting to the substrate, the carriermost often either evaporates leaving the suspended material on thesubstrate surface or the carrier hardens or cures. The thermalconditions and physical properties of the print material and substrate,along with the ambient conditions and nature of the print material,determine the specific rate at which the deposited print materialtransforms from a liquid to a solid, and hence the height and profile ofthe solidified deposited material.

If two adjacent droplets are applied to the substrate within a timeprior to the solidification of either or both droplets, the droplets maywet and coalesce together to form a single, continuous printed feature.Surface tension of the droplet material, temperature of the droplet atejection, ambient temperature, and substrate temperature are keyattributes for controlling the extent of droplet coalescence and lateralspreading of the coalesced material on the substrate surface. Theseattributes may be selected such that a desired feature size may beobtained.

However, one disadvantage of digital lithography is that due to therelatively large minimum drop size, currently on the order of 20-40 μm(micrometers) in diameter, device features manufactured by this processtend to be relatively large. For example, each pixel of a modern colorflat-panel display comprises a color filter located above or below agroup of thin film transistors. Each pixel comprises three sub-pixels,one for each color red, green, and blue, separated by a grid or frame.The frame is typically first formed, then filled with colored materialto form the sub-pixels. Current color pixels are in the neighborhood of100 μm wide. Each sub-pixel is on the order of 25-30 μm wide, and thewidth of each section of the frame is on the order of 10 μm. A digitallithographic process which produces drops no smaller than 20 μm wide isthus incapable of directly providing a droplet mask to form thesub-pixel frame. Thus, while it is known that available printing systemsare capable of very accurate drop placement, the relatively large dropsize has heretofore limited the scope of application of digitallithographic systems.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides a method for manufacturingmicro-electronic, opto-electronic, bio-electronic, or similar devicesemploying digital lithography, the devices having smaller feature sizesthan heretofore possible with digital lithography.

The process according to the present invention preferably uses a digitallithography system which deposits a phase change material. The phasechange material is deposited in a pattern to form an indirect mask.Subsequent steps of the process deposit or remove additional material toobtain the target features.

According to one aspect of the invention, a mask pattern is formed bydigital lithography on the surface of a substrate. The mask pattern isformed to include gaps which are equal in width to the desired width ofthe final feature to be formed (the target feature). This is possible,since digital lithography systems are capable of controllably depositingdroplets with an inter-droplet spacing less than a droplet diameter. Atarget material is deposited over (or between) the mask, by digitallithography, capillary action or other appropriate method. While themask material is well controlled in terms of dispersion, wetting, etc.,the target material is less well controlled. The target material fillsthe gaps formed in the mask. The mask acts as a form for the targetmaterial, overcoming issues associated with controlling the depositionof the target material. The target material may then be cured orhardened, if necessary, and the mask removed, producing the targetfeature.

According to a variation of this aspect of the present invention, thetarget material is a black matrix material (e.g., a pigmented polymer).The target features are a sub-pixel frame for a color display device.The gaps in the mask material are on the order of 10 μm wide, and theresulting width of the segments of the sub-pixel frame are accordinglyon the order of 10 μm wide, narrower than the diameter of the individualdroplets forming the mask.

According to another aspect of the present invention, the target featureis formed of layers of target material, each layer having a desiredproperty. For example, a multi-layered target feature may be comprisedof layers of hydrophilic material below layers of hydrophobic material.Such a target structure is useful in preventing the wetting of materialabutting against the target structure, for example the spreading of afirst fluid from one lateral side of the structure over its top and ontothe opposite lateral side of the structure.

The above is a summary of a number of the unique aspects, features, andadvantages of the present invention. However, this summary is notexhaustive. Thus, these and other aspects, features, and advantages ofthe present invention will become more apparent from the followingdetailed description and the appended drawings, when considered in lightof the claims provided herein.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings appended hereto like reference numerals denote likeelements between the various drawings. While illustrative, the drawingsare not drawn to scale. In the drawings:

FIG. 1A is a plan view of a color filter for a flat panel displayaccording to the prior art.

FIG. 1B is a profile view of the color filter for FIG. 1A.

FIG. 2A is a cross sectional view of a structure at a first stage in theprocess of forming a sub-pixel frame according to one embodiment of thepresent invention.

FIG. 2B is a plan view of the structure shown in FIG. 2A.

FIG. 2C is a cross sectional view of a structure at a second stage inthe process of forming a sub-pixel frame according to one embodiment ofthe present invention.

FIG. 2D is a plan view of the structure shown in FIG. 2C.

FIG. 2E is a cross sectional view of a structure at a third stage in theprocess of forming a sub-pixel frame according to one embodiment of thepresent invention.

FIG. 2F is a plan view of the structure shown in FIG. 2E.

FIG. 2G is a cross sectional view of a structure at a fourth stage inthe process of forming a sub-pixel frame according to one embodiment ofthe present invention.

FIG. 2H is a plan view of the structure shown in FIG. 2G.

FIG. 3 is a process flow diagram illustrating the steps involved in theformation of a sub-pixel frame according to one embodiment of thepresent invention.

FIG. 4A is a cross sectional view of a structure at a first stage in theprocess of forming a sub-pixel frame according to a second embodiment ofthe present invention.

FIG. 4B is a plan view of the structure shown in FIG. 4A.

FIG. 4C is a cross sectional view of a structure at a second stage inthe process of forming a sub-pixel frame according to the secondembodiment of the present invention.

FIG. 4D is a plan view of the structure shown in FIG. 4C.

FIG. 4E is a cross sectional view of a structure at a third stage in theprocess of forming a sub-pixel frame according to the second embodimentof the present invention.

FIG. 4F is a plan view of the structure shown in FIG. 4E.

FIG. 4G is a cross sectional view of a structure at a fourth stage inthe process of forming a sub-pixel frame according to the secondembodiment of the present invention.

FIG. 4H is a plan view of the structure shown in FIG. 4G.

FIG. 4I is a cross sectional view of a structure at a fifth stage in theprocess of forming a sub-pixel frame according to the second embodimentof the present invention.

FIG. 4J is a plan view of the structure shown in FIG. 4I.

FIG. 5 is a process flow diagram illustrating the steps involved in theformation of a sub-pixel frame according to one embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

With reference initially to FIGS. 1A and 1B, there is shown therein astructure of the type formed by one embodiment of the present invention.FIGS. 1A and 1B are illustrations of a portion of a color filter 10 fora plat-panel display. As mentioned, such a filter comprises a number ofpixels 12, each pixel being composed of three or more sub-pixels 14. Theactual geometry of the sub-pixels, such as triangular, striped,diagonal, etc. is not critical to the operation of the presentinvention, but will be discussed in further detail below. Sub-pixels 14are each primarily transparent to a specific color of light, such asred, green or blue. The individual sub-pixels 14 are separated by apixel frame 16. Pixel frame 16 is composed of a number of horizontal andvertical elements which form cavities, shown in FIG. 1B, for the receiptof material forming sub-pixels 14. For reference, it will be assumedthat the width w_(sp) of each sub-pixel is on the order of 25 to 30 μmand the width w_(f) of each pixel frame element is on the order of 10μm.

In order to form the structure illustrated in FIGS. 1A and 1B, specificsteps according to the present invention are described. FIGS. 2A through2H illustrate the structure at several intermediate stages of itsproduction according to a process illustrated in FIG. 3. While thefollowing description makes specific reference to the structureillustrated in FIGS. 2A through 2H, without making more specificreference thereto the description is following the sequence illustratedin FIG. 3.

With reference initially to FIG. 2A, the process begins with a suitablesubstrate 20, such as glass or plastic, such as poly ethylenenapthalate. onto which mask 22 is formed. Mask 22 is preferably formedby a digital lithographic process (and hence referred to as a “printpatterned mask”), and comprises individual or coalesced droplets of aphase change material such as stearyl erucamide wax (for example,Kemamide 180-based wax from Crompton Corporation of Middlebury, Conn.),or similar material which is well controlled in terms of print quality(i.e., droplet size and shape, solidification time, hardness ofsolidified structure, etc.) Examples of systems appropriate for theejection of droplets of phase change material include: ink-jet systems(such as disclosed in U.S. Pat. No. 4,131,899, which is incorporatedherein by reference), ballistic aerosol marking (BAM) devices (such asdisclosed in U.S. Pat. No. 6,116,718, which is incorporated herein byreference), acoustic ink printer (AIP) systems (U.S. Pat. No. 4,959,674,which is incorporated herein by reference), carrier-jet ejectors (asdisclosed in U.S. Pat. No. 5,958,122, which is incorporated by referenceherein), deflection-controlled ink-jet systems (such as disclosed inU.S. Pat. No. 3,958,252, which is incorporated herein by reference),etc. Such systems also include pattern transfer systems, such as:xerographic, ionographic, screen, contact, and gravure printing systems,etc.

While the embodiment discussed herein involves the formation of a printpatterned mask directly on substrate 20, it is within the spirit andscope of the present invention that such a mask, and the features formedthereby, be formed over other layers, such as layers containingpreviously formed devices. Accordingly, it may be necessary topositionally register the formation of mask 22. Registration isroutinely accomplished in digital lithographic systems by use offiduciary marks, digital imaging and processing, and processorcontrolled relative motion of the ejector and the substrate. The abilityto align the mask layer through image processing prior to patterning isa significant advantage of the digital-lithographic process over otherpatterning methods.

For illustrative purposes, FIG. 2A shows three individual, adjacent butnot contiguous digital lithographic masking elements (i.e., droplets)24, 26, 28. A plan view of this arrangement is illustrated in FIG. 2B.For the purposes of illustration, droplets 24, 26, 28 will be assumed tobe on the order of 25-30 μm in diameter, corresponding to the width of asub-pixel of a color flat-screen display. However, the width of theindividual print patterned mask features may be an arbitrary sizegreater than or equal to the minimum diameter of a droplet ejected bythe digital lithography system used, depending on the feature and deviceto be formed. For example, to achieve a width greater than the diameterof a single droplet, adjacent droplets may be deposited such that theycoalesce into a single feature as they solidify. Furthermore, theedge-to-edge spacing between droplets is assumed for the purposes ofillustration to be on the order of 10 μm, corresponding to the width ofan element of a sub-pixel frame. However, according to the presentinvention, the spacing between individual print patterned mask featuresmay be an arbitrary size, limited only by the resolution of theprinthead or stage employed by the digital lithography system, and afunction of the feature and device to be formed.

In select instances, adhesion promoters of the type commonly used withphotoresist materials in the semiconductor processing art provideimproved adhesion of the phase change material. For example,hexamethyldisilizane (HMDS) is used for chemically drying the substrateto promote adhesion. Other methods are annealing and plasma cleaningfollowed by an HMDS coating in order to clean and prepare the surfacefor photoresist adhesion.

Considering that the elements of the sub-pixel frame (FIGS. 1A, 1B) areassumed to be on the order of 10 μm wide, and the digital lithographicmasking elements (i.e., the individual droplets) are typically muchwider (e.g., on the order of 25-30 μm), the digital lithographic maskingelements do not make feasible feature masks. Accordingly, the maskingelements are not used to directly mask such features, but are insteadused as indirect masks.

According to this embodiment, a black matrix material is deposited overselected portions of mask 22, filling the interstices between thedigital lithographic masking elements 24, 26, 28, and forming blackmatrix regions 30, 32, as illustrated in FIG. 2C. A plan view of thestructure at this point in the process is illustrated in FIG. 2D. Theblack matrix material is typically a curable polymer with suspended darkpigment such as a polyimide dissolved or suspended in an organicsolvent. The black matrix material can either be thermally curable orphotocurable. For thermally curable materials, it is possible topartially cure the material to improve its resistance to attack bysolvents at a temperature, for example 100 C, significantly lower thanits final curing temperature, for example 150 to 200 C. Certainmaterials are less well controlled in terms of print quality thanothers. For example, if deposited directly on a substrate, uncured blackmatrix material tends to wet and spread across the substrate surface, inflattened, wide, and uncontrolled geometries. Accordingly, mask 22, andmore precisely the digital lithographic masking elements 24, 26, 28,serve to constrain the dispersal of the black matrix material until itis cured, much like a form.

The black matrix material can be deposited using a number of techniques.If the mask material completely covers each pixel opening then the blackmatrix material can be coated onto the substrate by dip coating or byblade, or slit, coating. An alternative method is to fill theinterstices by capillary filling as the masking elements may in certainembodiments form a set of open fluidic channels on the substrate. Inthis case, an appropriate volume of the liquid black matrix material canbe deposited onto a small portion or portions of the substrate andmaintained in liquid form in order to allow it to flow into the openchannels across a larger portion of the substrate. This method canminimize printing of the black matrix, since the capillary or wickingforces provide an even distribution of the black matrix fluid over thearray.

According to one embodiment, the black matrix material is then cured byraising its temperature. To accomplish this, the structure may be placedin an oven at a desired temperature for a selected length of time. Thetemperature needed to cure the black matrix material must be lower thanthe melting temperature of the phase change material forming the digitallithographic masking elements 24, 26, 28, since the mask 22 must remainin place until the black matrix material is fully cured. Accordingly,the melting temperature of the phase change material must not be so highas to make it's ejection from the digital photolithographic systemproblematic, nor so low as to interfere with the curing of the blackmatrix material. An example of the conditions for an appropriate bake ofthe black matrix material are 50° C. to 60° C. for 15 to 20 minutes (butwill ultimately depend on the actual selection of the black matrixmaterial).

According to an alternate embodiment, the black matrix material may beanother phase-change material that has a higher melting point than themask material and can be selectively removed. For example, Corsair Wax(Xerox Corporation, Stamford, Conn.) has a high melting temperature anddoes not dissolve as readily in solvent as the aforementioned Kemamidewax. Thus, when tinted, the Corsair Wax may serve as a black matrixmaterial. Furthermore, hardenable colloidal solutions (i.e., those thatharden as the carrier solvent evaporates and leave behind the solidmaterial such as nano-particles) can be processed as a liquid and dry asa solid. Thus, an appropriate colloidal solution bearing tinted solidsmay be deposited to form the black matrix. In each case, however, curingis replaced with a corresponding process (i.e., cooling, evaporation)for producing a hardened black matrix.

According to a still further alternate embodiment, the black matrixmaterial is a thermally curable polymer with suspended dark pigment. Theprocessing of the black matrix material in this case involves carefulcontrol of the degree of curing, or cross-linking, in the black matrixfilm. After deposition of the black matrix material, the film ispartially cured to a point to permit patterning by development instandard TMAH baths. These types of black matrix materials arecommercially available, such as DARC 400 from Brewer Science (Danvers,Mass.).

Once the black matrix material is hardened, and self-supporting blackmatrix regions 30, 32 are formed, the mask 22 may be removed. One of avariety of solvents may be used for this purpose, such as SVC-28(MicroChem Corporation, Newton, Mass.). SVC-28 is a debonding solutionmanufactured by Rohm-Hass. The active ingredients are dipropylene glycolmonomethyl ether, citrus distallate, synthetic isoparraffinichydrocarbon, and aliphatic hydrocarbon. Where the black matrix materialis a polyimide-based material that is dissolved or suspended in organicsolvents similar to positive photoresist material, a negativephotoresist stripper may selectively remove the masking elements whileleaving the cured black matrix material unaffected. (Thus, the solventused will depend upon the actual selection of the materials forming thedigital lithographic masking elements and the black matrix regions.) Thesolvent selectively removes the masking material but not the cured blackmatrix material nor the substrate (or any devices or layers on which theaforementioned structure is formed). This is illustrated incross-section in FIG. 2E and in plan view in FIG. 2F.

In certain circumstances, it may be desirable to form attack points forthe removal of the digital lithographic masking elements. These arepoints where the solvent is provided greater access to the surface ofthe masking elements. Once the black matrix material is cured by therelatively low temperature bake (referred to as a “soft bake”), thestructure may be subjected to a second, higher temperature bake, on theorder of 120° C. to 150° C. for 5 to 15 minutes (referred to as a “hardbake”). The hard bake causes a partial melting of the masking elements,and a consequent disconnection of the masking material from the surfaceof the cured black matrix material. The gap thus formed between theblack matrix material and the masking material allows the solvent betteraccess to the masking material, and hence a more thorough and completeremoval of that material from the structure. However, the hard bake isan optional step in the process.

After removal of the mask, some formulations of the black matrix willneed a further curing step to fully harden the material. Typicaltemperatures for such steps are 150 C or higher.

At this point the structure comprises robust black matrix structures 30,32 which may serve numerous purposes. First, such structures may serveas exposure or etch masks for layers formed thereunder (not shown).While described above as being formed of a black matrix material,structures 30, 32 may alternatively be formed of other materials whichexhibit selected properties, such as electrical, thermal or opticalconductance or insulation, or a desired degree of rigidity orflexibility. Accordingly, a wide variety of structures may thus beproduced, where the structures 30, 32 may be electrical contacts,conductors, channels, thermal or optical filters, micromechanicalactuators, etc. However, in keeping with the aforementioned description,and without limiting the scope of the present invention, it will beassumed below that black matrix structures 30, 32 serve as elements of asub-pixel frame.

The removal of the masking material results in the formation of wells 34in the regions between the self-supporting black matrix material regions30, 32, as shown in FIG. 2E. Wells 34 are bounded on all sides by theblack matrix material, as illustrated in FIG. 2F. Thus, wells 34 formconvenient receptacles for color filter material. The color filtermaterial may comprise a pigmented polymer, for example. The pigment mayselectively permit the transmission of red, green or blue light. Theappropriate color filter material may thus be deposited, for example bya digital lithographic system, into selected wells to form sub-pixelsfor the color filter, as shown in FIG. 2G. For example, an ink jetprinting system may be employed to first fill every first, fourth,seventh, etc., well with a red tinted filter material. That same systemmay then be employed to deposit a green tinted filter material in everysecond, fifth, eighth, etc., well. And likewise, a blue tinted colorfilter material may be deposited in a third pass over the structure intoevery third, sixth, ninth, etc., well. The color filter material istypically thermally cured to harden the film. The color filter withfilled wells 36, 38, 40 shown in FIG. 2H is thus obtained.

In the deposition of the color filter materials, care must be taken toprevent cross-contamination of the various individual color filtermaterials. For example, any introduction of the green color filtermaterial into the well containing the red color filter material willresult in poor color separation of the final display. Such crosscontamination can occur due to inaccuracies in the filling of the wells,from physical disruption of the color filter structure, from inadequatesub-pixel frame structure, and from wetting of the color filter materialcausing it to spread out of its designated well and into surroundingwells. One advantage of the present invention is that the cross sectionsof the sub-pixel frame elements (the black matrix features) will tend tobe concave or curve inward toward the top of the well. This stands insharp contrast to prior art structures, which typically have a profiletapering outward toward the top of the well, which in fact promoteswetting of the color filter material into neighboring wells. It will beappreciated that the degree of curvature or concavity of the sub-pixelframe elements may be controlled by controlling the degree of spreadingof the print patterned masking elements.

Furthermore, according to another embodiment of the preset invention,the black matrix material may be “engineered” to have desiredhydrophobic or hydrophilic properties along its elevation to assist inpreventing such wetting-induced cross-contamination. The black matrixmaterial may be formed as a multiple layered structure with lower layersmore hydrophilic and upper layers more hydrophobic. The black matrixmaterial may be deposited in layers, with intermediate curing orhardening to avoid intermixture of the layers, or may be deposited as asingle compound, then treated, for example by thermal annealing, toseparate the materials into distinct layers. Such a structureadvantageously reduces the tendency of the color filter material to wetacross sub-pixel frame boundaries.

A structure produced by a process according to this aspect of thepresent invention is shown in FIGS. 4A through 4J. FIG. 5 illustratesthe process flow according to this embodiments. Initially, the structureis quite similar to that described above with regard to FIGS. 2A and 2B.With reference to FIG. 4A, a suitable substrate 70 is selected, such asglass, silicon, fused silica, quartz, MgO, sapphire, glass or plastic,such as poly ethylene napthalate. In the case in which a color filterpanel is to be produced, the substrate will typically be a transparentmaterial, such as glass or plastic. Print patterned mask 72 is formed onsubstrate 70. Print patterned mask 72 is preferably formed by a digitallithographic process, and comprises a number of spaced-apart maskfeatures 74, 76, 78. Adhesion promoters may be employed and alignmentmay be accomplished as previously discussed. FIG. 4B is a plan view ofthe structure at this point in its fabrication.

With reference now to FIG. 4C, a first black matrix material isdeposited over selected portions of mask 72, partially filling theinterstices between the masking elements 74, 76, 78, and forming firstblack matrix regions 80, 82. The first black matrix material is selectedto be hydrophilic, or relatively wettable by the solvent of the colorfilter material, with the aim that the first black matrix material actsto retain the color filter material within its wells. The structure atthis point is baked at a temperature sufficient to cure the first blackmatrix material but below the melting point of the masking elements 74,76, 78, the so-called soft bake. A plan view of the structure at thispoint is illustrated in FIG. 4D.

With reference now to FIG. 4E, a second black matrix material isdeposited over first black matrix regions 80, 82, further partiallyfilling the interstices between the masking elements 74, 76, 78, andforming second black matrix regions 84, 86. (The second black matrixmaterial does not necessarily need to be “black” or even opaque. It maybe a material that is solution processable that is hydrophobic or makesthe surface of the first material hydrophobic.) The second black matrixmaterial is selected to be hydrophobic with the aim that the secondblack matrix material acts to prevent wetting of the color filtermaterial over the sub-pixel frame elements. The structure at this pointis again soft baked to cure the second black matrix material. A planview of the structure at this point is illustrate in FIG. 4F.

In the case of using a bilayer structure to form the structure for theblack matrix, one of the layer could have a different transparency thanthe other. This structure is useful for cases where it may be difficultto achieve the appropriate difference in wettability if both layers arepigmented to the same extent. For example, the hydrophobic upper layercould be transparent if the optical density of the lower hydrophiliclayer is high enough.

At this point, mask 72 may be removed, with or without the optional hardbake to create supplemental attack points. The solvent used for removingmask 72 will depend upon the actual selection of the material formingthe digital lithographic masking elements, but may include theaforementioned tetrahydrofuran or heated SVC-28. (In the case that mask72 is a wax, at a temperature above the melting point of the wax, SVC-28will remove the wax from the surface even though SVC-28 is a surfactantin which the wax does not readily dissolve.) The solvent selectivelyremoves the masking material but not the first or second cured blackmatrix materials nor the substrate (or any devices or layers on whichthe aforementioned structure is formed). This is illustrated incross-section in FIG. 4G and in plan view in FIG. 4H.

Although the material forming the lower and upper portions of theremaining black matrix structures are different, the conditions for thecuring of the layers allows the layers to structurally bond, formingstructurally robust, free-standing bi-layer black matrix materialstructures 80/84, 82/86 in which the lower regions are hydrophilic andthe upper regions are hydrophobic. These structures define wells 88, asshown in FIG. 4G. Wells 88 are then filled with color filter material,as previously discussed and shown in FIG. 4I. The color filter withfilled wells 90, 92, 94 shown in FIG. 4J is thus obtained.

Generally, multilayered structures 80/84, 82/86 may by engineered for avariety of desirable attributes, and capability not readily availablefrom processes known in the art. For example, in the case where suchstructures serve as micromechanical actuators, they may be provided witha more flexible material at their base and a less flexible material attheir tips. In the case where such structures are bioelectrical devices,they may be provided with greater reactivity to a material at the basethereof and a lesser reactivity to a material at the tip thereof, and soon.

While a plurality of preferred exemplary embodiments have been presentedin the foregoing detailed description, it should be understood that avast number of variations exist, and these preferred exemplaryembodiments are merely representative examples, and are not intended tolimit the scope, applicability or configuration of the invention in anyway. For example, while the process of the present invention has beendescribed to form a sub-pixel frame, the process may be used to form awide variety of other structures, such as exposure or etch masks,contacts or elements of microelectronic, optoelectronic, bioelectronic,etc., devices, and other physical structures. Furthermore, whilereferences to matrix material herein have been to a “black” matrixmaterial, the actual color of the material is not critical, and thedegree of opacity of the material in its final state is a function ofthe design targets of the device being fabricated. Accordingly, theforegoing detailed description provides those of ordinary skill in theart with a convenient guide for implementation of the invention, andcontemplates that various changes in the functions and arrangements ofthe described embodiments may be made without departing from the spiritand scope of the invention defined by the claims thereto.

1. A method of forming a sub-pixel frame for a display device over asubstrate, comprising the steps of: depositing a phase change materialover the substrate; the phase change material deposited as dropletsusing a printing system comprising a printhead, such that a plurality ofsaid droplets are deposited so as to coalesce; the printhead includingat least one ejector for ejecting the phase change material in liquidphase; the phase change material deposited in a first printed patternsuch that the first printed pattern of phase change material remainsfollowing a change from liquid phase to solid phase of the phase changematerial; the first printed pattern defining gaps; depositing a targetmaterial at least partially into the gaps to form target materialfeatures; hardening the target material features to form a sub-pixelframe; and removing the phase change material, leaving the sub-pixelframe on the substrate, the sub-pixel frame defining at least one wellfor receiving material deposited therein.
 2. The method of claim 1,wherein the target material is deposited using a printing systemcomprising a printhead which includes at least one ejector for ejectingthe target material in liquid phase, and the target material isdeposited so as to form a second pattern such that the target materialis primarily introduced into and fills the gaps defined by the firstprinted pattern.
 3. The method of claim 1, wherein the step of hardeningthe target material comprises hardening by heating the target material.4. The method of claim 3 wherein the temperature to which the targetmaterial is heated is below the melting temperature of the phase changematerial.
 5. The method of claim 4, wherein following the step ofhardening the target material, the target material and phase changematerial are heated to a temperature exceeding the melting temperatureof the phase change material.
 6. The method of claim 1, wherein the stepof removing the phase change material comprises a single step ofapplying a solvent which removes the phase change material but does notaffect the target material.
 7. The method of claim 1, further comprisingthe step of depositing a supplementary target material over the targetmaterial prior to the step of removing the phase change material.
 8. Themethod of claim 7, further comprising the step of hardening thesupplementary target material to form a supplementary portion of thesub-pixel frame prior to removal of the phase change material.
 9. Themethod of claim 8, wherein the step of hardening the supplementarytarget material is accomplished by heating the supplementary targetmaterial.
 10. The method of claim 9 wherein the temperature to which thesupplementary target material is heated is below the melting temperatureof the phase change material.
 11. The method of claim 1, wherein thesub-pixel frame is enclosed on all lateral sides, and the substrateforms a base of the sub-pixel frame, such that the sub-pixel frame maybe substantially filled and contain a material deposited therein. 12.The method of claim 11, further comprising the step of depositing amaterial into the sub-pixel frame.
 13. The method of claim 12, whereinthe material is a hardenable pigmented liquid.
 14. The method of claim1, wherein the target material features are formed to have a generallyconcave cross section.
 15. The method of claim 1, wherein adjacentsub-pixel frames are formed to have cross sections which curve inwardtoward each other, the distance between the adjacent sub-pixel framesdecreasing as the distance away from the substrate increases.
 16. Amethod of forming a sub-pixel frame for a color filter, comprising thesteps of: depositing a phase change material over a substrate; the phasechange material deposited as droplets using a printing system comprisinga printhead, such that a plurality of said droplets are deposited so asto coalesce; the printhead including at least one ejector for ejectingthe phase change material in liquid phase; the phase change materialdeposited in a first printed pattern such that the first printed patternof phase change material remains following a change from liquid phase tosolid phase of the phase change material; the first printed patterndefining gaps; depositing a black matrix material; the black matrixmaterial deposited using a printing system comprising a printhead; theprinthead including at least one ejector for ejecting the black matrixmaterial in liquid phase; the black matrix material deposited in asecond printed pattern such that the black matrix material isselectively introduced into the gaps defined by the first printedpattern; heating the black matrix material such that the black matrixmaterial hardens to form a sub-pixel frame, wherein the temperature towhich the black matrix material is heated is below the meltingtemperature of the phase change material; heating the black matrixmaterial and phase change material to a temperature exceeding themelting temperature of the phase change material; removing the phasechange material, leaving the sub-pixel frame on the substrate; anddepositing a hardenable pigmented fluid, using a printing systemcomprising a printhead which includes at least one ejector for ejectingthe hardenable pigmented fluid in liquid phase, in a third pattern, suchthat the hardenable pigmented fluid is deposited into interstitialregions in the sub-pixel frame.
 17. The method of claim 16, wherein theblack matrix material is hydrophilic, and further comprising the step ofdepositing a supplementary black matrix material over the sub-pixelframe prior to the step of removing the phase change material, thesupplementary black matrix material being hydrophobic.
 18. The method ofclaim 16, wherein the black matrix material features are formed to havea generally concave cross section.
 19. The method of claim 16, whereinadjacent black matrix material features are formed to have crosssections which curve inward toward each other, the distance between theadjacent black matrix material features decreasing as the distance awayfrom the substrate increases.
 20. The method of claim 16, wherein thestep of depositing a black matrix material comprises the step ofdepositing first and second materials, the first material beingrelatively more hydrophilic than the second material.